1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, an electrophotographic image forming apparatus and a process cartridge. To be more specific, the present invention relates to an electrophotographic photoreceptor that is durable and can form high-quality images, an electrophotographic image forming apparatus using the electrophotographic photoreceptor, and a process cartridge used for the electrophotographic image forming apparatus.
2. Description of Related Art
In recent years, there has been a need for smaller and maintenance-free electrophotographic image forming apparatuses as well as those with higher print output performance. Along with such needs, there has also been an increasing need for drum photoreceptors with smaller diameter (smaller size) and more durability, which are electrophotographic photoreceptors used in electrophotographic image forming apparatuses. Typical electrophotographic photoreceptors are organic photoreceptors (hereinafter also referred to as simply “photoreceptors”), and the photosensitive layer thereof, which is composed of a charge transfer material, a binder resin and the like, is prone to abrasion caused by mechanical load.
Photoreceptors deteriorate with repetitive image forming due to abrasion caused by friction with a cleaning blade. Moreover, the electric properties such as charging property and photosensitivity also deteriorate with repetitive charging and repetitive exposure. Such deterioration causes image defects such as low image density and smudgy background. Further, local flaws caused by abrasion of a photoreceptor surface cause image defects such as stripe due to imperfect cleaning, which results in decreased lifespan of photoreceptors.
To improve the durability of photoreceptors, it is required to improve the abrasion resistance of photoreceptors. For this reason, techniques of providing a surface protection layer on the surface of a photosensitive layer have been developed. One of techniques known in the art for providing a surface protection layer with high abrasion resistance is to add a curable binder resin and inorganic fine particles to a surface protection layer.
On the other hand, for preventing degradation of the electric properties of a surface layer, there is a technique known in the art of adding a charge transfer material so as to impart charge transfer capability to the surface protection layer.
However, conventional surface protection layers suffer from low compatibility between the low-molecular-weight charge transfer material and the curable binder resin. This causes inhibition of charge migration in the surface protection layers and raises a residual potential, which results in a problem of image defects such as low image density. Further, another problem with conventional surface protection layers is that the plasticization effect of the low-molecular weight charge transfer material decreases the abrasion resistance of the surface protection layers.
One of techniques known in the art for solving these problems is to add inorganic fine particles surface-treated with a hole transporting group-containing surface treatment agent to a surface protection layer (e.g. see JP 2010-134071A). This technique is to add inorganic fine particles surface-treated with a hole transporting group-containing alkoxysilane compound to a surface protection layer. By this feature, the inorganic fine particles are uniformly dispersed in the surface protection layer. As a result, the abrasion resistance is improved by the filler effect of the inorganic fine particles and a curable binder resin, and image blur in a hot and humid environment due to discharge products such as ozone and nitrogen oxides is prevented. Further, since charge (hole) migration is not inhibited in the surface protection layer due to the hole transporting group of the surface treatment agent, this technique is also advantageous in that the sensitivity properties are not impaired. However, a problem with this technique is an image memory effect in a hot and humid condition. As used herein, an image blur refers to a blur in toner images due to disordered electrostatic latent images, which are caused by hydrophilization of a photoreceptor surface by discharge products such as ozone and nitrogen oxides.